When you hack the net, some people might get upset at your actions and come after you, usually by backtracing a log of some kind.
So you should prepare by setting up a Shell on any computer you have admin access to. Your own computer is fine.

After you set up a Shell on a computer you set that shell to Trap

Trap, which is an alternate function of a Shell other than Overflow, is a function which lets you forkbomb a computer that is trying to hack you.

Make sure to connect to your own computer then simply click Trigger shortly after you see you're being hacked. You can watch your computer's logs for his activity and watch him hack into you, which can be repelled with the trap.

There will be a notification on your screen saying incoming connection as well as the beep you hear when a passive trace is in effect if you hack someone else.

If you were too late to trigger your shell, your computer will be hit with a forking Forkbomb.

Forkbomb is a command which floods the ram of the PC its used on. As soon as it starts, you'll have roughly 5 seconds to act.

To stop a forkbomb, you must type ps to find the process ID of the forkbomb running on your computer.

When you find the process ID of the forkbomb running, type kill [ps#]

This will stop the forkbomb and free up your ram again.

Assuming you were able to not get hit by a forkbomb by someone hacking you, you're able to freely attack.
Check your logs for the computer that hit you and type connect and the IP address you found in the logs.
You go in and use a forkbomb on them to take down the computer, which I reccomend you do after removing logs and target files in the computer you're attacking.
After that its generally the same as you learned in the tutorial.

As a sidenote for if theres ever a multiplayer function added, if you really want to mess with them rather than hitting them with a forkbomb,you can type OpenCDtray while connected to their PC to open their CD tray, and then CloseCDtray to close it again. Using tab to autofinish the commands helps to save time and using the arrow keys lets you use that to continue annoying them rather than hacking.

You can test that on your own computer by connecting to your PC node and typing it in.
Same with Forkbomb and finding the processing number if you want to practice.

Created on 6/9/16 19:53 EST - Only current purpose of the guide is to be a refrence in deflecting Naix's counterhack in retort to your actions. Though its been predicted that future DLC and a multiplayer function will be added into the game. DLC may include more hackers going after you and a need to use the forkbomb command to take down computers.

Edited on 7/2/16 23:32 EST - Clarifying instructions to preventing the stress of dealing with Naxi to say you need to be connected to the computer being actively traced in order to counter attackers. As you yourself are being hacked, you will want to connect to your own computer, not anyone elses or no computer at all.

Edited on 9/28/16 18:23 EST - Got a comment saying Naxi's activities can be watched through your logs so I added that little note in. Thats useful for when he actually tries to hack into your computer, you know where he's coming from.
As a side note, there was an official announcement of multiplayer, where you hack into systems with other people, and theres new tools in it, like one that measures Ram usage. Feel free to look into it on your own if interested.

Deflecting Naxi's attack does not prevent you from hacking him back in and removing his system file as long as you do that before finishing any other missions. Emailing him a swear word for an achievement (remember to make it lowercase so it works) may still work if you do this. You can access the /el/ jobs if you don't get hacked. You just have to hack Naxi and remove his x-system file.